Mild hydrocracking with a catalyst containing an intermediate pore molecular sieve

ABSTRACT

Mild hydrocracking is accomplished with a catalyst containing an intermediate pore molecular sieve, such as silicalite or a ZSM-5 type zeolite.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 711,452 filed Mar. 13, 1985 pending, and also acontinuation-in-part of U.S. patent application Ser. No. 715,510 filedMar. 22, 1985, now U.S. Pat. No. 4,600,498, both of which are acontinuation-in-part of U.S. patent application Ser. No. 531,924, filedSept. 13, 1983, now U.S. Pat. No. 4,517,074, which is a divisionalapplication of U.S. patent application Ser. No. 84,761, filed Oct. 15,1979, and now U.S. Pat. No. 4,419,271. This application is also acontinuation-in-part of U.S. patent application Ser. No. 699,919 filedFeb. 8, 1985, now U.S. Pat. No. 4,610,973, which is a continuation ofU.S. patent application Ser. No. 531,924, filed Sept. 13, 1983, now U.S.Pat. No. 4,517,074, which is a divisional application of U.S. patentapplication Ser. No. 84,761, filed Oct. 15, 1979, and now U.S. Pat. No.4,419,271.

BACKGROUND OF THE INVENTION

The invention relates to a process for mild hydrocracking hydrocarbonoils. More particularly, the invention relates to a mild hydrocrackingcatalytic process for treating vacuum gas oils and residuum hydrocarbonfeedstocks.

In the refining of hydrocarbon oils, it is often desirable to subjectthe hydrocarbon oil to catalytic hydroprocessing. One such process ishydrocracking, a process wherein, in the typical instance, a gas oil orresiduum feedstock is passed with hydrogen through a bed of catalystactive for cracking relatively high molecular weight compounds to moredesirable, relatively low molecular weight compounds of lower boilingpoint. In addition, because the catalyst has hydrogenation activity, thecracked products are saturated by hydrogenation while organosulfur andorganonitrogen compounds in the feed are converted to hydrogen sulfideand ammonia, respectively, both of which are usually removed ingas-liquid separators. Thus, the advantage of hydrocracking lies in theconversion of a sulfur-containing and/or nitrogen-containing gas oilfeed, boiling, for example, mostly above about 700° F., to a relativelysulfur and nitrogen-free product of boiling point below 700° F., such asgasoline, jet fuel, diesel fuel, and mixtures thereof.

Recently, attention has been directed to "mild hydrocracking." The costof constructing a hydrocracking unit operating at high pressures isquite significant and poses a major economic obstacle to its use.Accordingly, interest has developed in converting existinghydroprocessing units, such as hydrotreating or hydrodesulfurizationunits, into hydrocracking units. It is realized, of course, thathydrotreating units and the like are not normally designed for optimumhydrocracking conditions, and specifically, for the high pressuresusually employed in commercial hydrocracking, i.e., above 1,500 p.s.i.g.Nevertheless, there is still an advantage if even some hydrocracking canbe achieved under the low pressure constraints of typical hydrotreatingor hydrodesulfurization units, and the challenge to the art is todiscover hydrocracking catalysts having sufficient activity and activitymaintenance to be commercially useful under such mild hydrocrackingconditions.

Therefore, an aim of the art is to provide a mild hydrocracking catalysthaving a high activity, selectivity and stability. Activity may bedetermined by comparing the temperature at which various catalysts mustbe utilized under otherwise constant mild hydrocracking conditions withthe same feedstock so as to produce a given percentage (usually between10 and 50 volume percent) of products boiling at or below 700° F. Thelower the temperature for a given catalyst, the more active such acatalyst is for mild hydrocracking. Alternatively, activity may bedetermined by comparing the percentages of products boiling at or below700° F. when various catalysts are utilized under otherwise constantmild hydrocracking conditions with the same feedstock. The higher thepercentage of 700° F.-minus product converted from the components in thefeedstock boiling above 700° F. for a given catalyst, the more activesuch a catalyst is in relation to a catalyst yielding a lower percentageof 700° F.-minus product. Selectivity of a mild hydrocracking catalystmay be determined during the foregoing described activity test and ismeasured as that percentage fraction of the 700° F.-minus productboiling in the range of middle distillate or midbarrel products, i.e.,300° F.-700° F. Stability is a measure of how well a catalyst maintainsits activity over an extended time period when treating a givenhydrocarbon feedstock under the conditions of the activity test.Stability is generally measured in terms of the change in temperaturerequired per day to maintain a 40 volume percent or other givenconversion (usually less than 50 volume percent).

SUMMARY OF THE INVENTION

The invention provides a mild hydrocracking process using a catalystcontaining at least one active hydrogenation metal component incombination with an intermediate pore molecular sieve. In oneembodiment, a vacuum gas hydrocarbon oil is mildly hydrocracked, withconcomitant desulfurization and denitrogenation, by contact with theintermediate pore molecular sieve catalyst under mild hydrocrackingconditions correlated so as to convert about 10 to about 50 volumepercent of the oil fraction boiling above 700° F. to hydrocarbonproducts boiling at or below about 700° F.

The most preferred intermediate pore molecular sieve for use in theinvention is silicalite or a similarly active microporous crystallinesilica. Second only to such materials in preference are ZSM-5-typezeolites.

One of the most important discoveries in the invention is thatsilicalite, ZSM-5, and related materials are useful under the relativelyunfavorable conditions of mild hydrocracking. ZSM-5, of course, is wellknown for its activity in cracking straight chain and slightly branchedchain paraffins, and a similar discovery pertaining to silicalite wasdisclosed in U.S. Pat. No. 4,428,862 issued to the present inventor andTimothy L. Carlson. However, since the pore sizes of these molecularsieves exclude large, ring-shaped organic compounds as well as heavilybranched paraffins, they are generally considered unsuitable forhydrocracking under the favorable conditions of high pressure. Thus, itwas a distinct surprise to discover in the present invention that thesemolecular sieves proved highly useful under the unfavorable low pressureconditions existing in mild hydrocracking.

DETAILED DESCRIPTION OF THE INVENTION

The invention is directed to a mild hydrocracking process using acatalyst comprising one or more active hydrogenation metals or compoundsthereof and an intermediate pore molecular sieve having crackingactivity and a pore size between about 5.0 and about 7.0 angstroms,preferably between about 5.0 and 6.0 angstroms. The term "molecularsieve" as used herein refers to any material capable of separating atomsor molecules based on their respective dimensions. The preferredmolecular sieve is a crystalline material, and even more preferably, acrystalline material of relative uniform pore size. The term "pore size"as used herein refers to the diameter of the largest molecule that canbe sorbed by the particular molecular sieve in question. The measurementof such diameters and pore sizes is discussed more fully in Chapter 8 ofthe book entitled "Zeolite Molecular Sieves" written by D. W. Breck andpublished by John Wiley & Sons in 1974, the disclosure of which book ishereby incorporated by reference in its entirety.

The intermediate pore crystalline molecular sieve which forms one of thecomponents of the catalyst of the invention may be zeolitic ornonzeolitic, has a pore size between about 5.0 and about 7.0 angstroms,possesses cracking activity, and is normally comprised of 10-memberedrings of oxygen atoms. The preferred intermediate pore molecular sieveselectively sorbs n-hexane over 2,2-dimethylbutane. The term "zeolitic"as used herein refers to molecular sieves whose frameworks are formed ofsubstantially only silica and alumina tetrahedra, such as the frameworkpresent in ZSM-5 type zeolites. The term "nonzeolitic" as used hereinrefers to molecular sieves whose frameworks are not formed ofsubstantially only silica and alumina tetrahedra. Examples ofnonzeolitic crystalline molecular sieves which may be used as theintermediate pore molecular sieve include crystalline silicas,silicoaluminophosphates, chromosilicates, aluminophosphates, titaniumaluminosilicates, titaniumaluminophosphates, ferrosilicates, andborosilicates, provided, of course, that the particular material chosenhas a pore size between about 5.0 and about 7.0 angstroms.

The silicoaluminophosphates which may be used as the intermediate porecrystalline molecular sieve in the catalyst of the invention arenonzeolitic molecular sieves comprising a molecular framework of [AlO₂], [PO₂ ], and [SiO₂ ] tetrahedral units. The different species ofsilicoaluminophosphate molecular sieves are referred to by the acronymSAPO-n, where "n" denotes a specific structure type as identified byX-ray powder diffraction. The various species of silicoaluminophosphatesare described in detail in U.S. Pat. No. 4,440,871, the disclosure ofwhich is hereby incorporated by reference in its entirety, and one useof these materials is disclosed in U.S. Pat. No. 4,512,875, hereinincorporated by reference in its entirety. The silicoaluminophosphateshave varying pore sizes and only those that have pore sizes betweenabout 5.0 and 7.0 angstroms may be used as the intermediate poremolecular sieve in the catalyst of the invention. Thus, typical examplesof silicoaluminophosphates suitable for use in the catalyst are SAPO-11and SAPO-41. The silicoaluminophosphates are also discussed in thearticle entitled "Silicoaluminophosphate Molecular Sieves: Another NewClass of Microporous Crystalline Inorganic Solids" published in theJournal of American Chemical Society, Vol. 106, pp. 6093-6095, 1984.This article is hereby incorporated by reference in its entirety.

Other nonzeolitic molecular sieves which can be used as the intermediatepore crystalline molecular sieve in the catalyst of the invention arethe crystalline aluminophosphates. These molecular sieves have aframework structure whose chemical composition expressed in terms ofmole ratios of oxides is Al₂ O₃ : 1.0±0.2 P₂ O₅. The various species ofaluminophosphates are designated by the acronym AlPO₄ -n, where "n"denotes a specific structure type as identified by X-ray powderdiffraction. The structure and preparation of the various species ofaluminophosphates are discussed in U.S. Pat. Nos. 4,310,440 and4,473,663, the disclosures of which are hereby incorporated by referencein their entireties. One useful crystalline aluminophosphate is AlPO₄-11.

Two other classes of intermediate pore molecular sieves for use in theinvention are borosilicates and chromosilicates. Borosilicates aredescribed in U.S. Pat. Nos. 4,254,297, 4,269,813, and 4,327,236, thedisclosures of all three of which are hereby incorporated by referencein their entireties. Chromosilicates are described in detail in U.S.Pat. No. 4,405,502, the disclosure of which is also hereby incorporatedby reference in its entirety.

Another class of intermediate molecular sieve for use in the inventionare the titanium aluminophosphates. Such materials are described ingreater detail in U.S. Pat. No. 4,500,651, herein incorporated byreference in its entirety, and are designated by the acronym TAPO-nwhere the "n" is an arbitrary number specific to a given member of theclass. One such material which has a pore size of intermediatedimensions is TAPO-11.

Yet another class of molecular sieves herein are the titaniumaluminosilicates, particularly those described under the acronym TASO-nwhere, again, the "n" is an arbitrary number specific to a given memberof the class. One such material having a pore size of intermediatedimension is TASO-45.

The most useful zeolites for use in the invention are the crystallinealuminosilicate zeolites of the ZSM-5 type, such as ZSM-5, ZSM-11,ZSM-12, ZSM-23, ZSM-35, ZSM-38, and the like, with ZSM-5 beingpreferred. ZSM-5 is a known zeolite and is more fully described in U.S.Pat. No. 3,702,886 herein incorporated by reference in its entirety;ZSM-11 is a known zeolite and is more fully described in U.S. Pat. No.3,709,979, herein incorporated by reference in its entirety; ZSM-12 is aknown zeolite and is more fully described in U.S. Pat. No. 3,832,449,herein incorporated by reference in its entirety; ZSM-23 is a knownzeolite and is more fully described in U.S. Pat. No. 4,076,842, hereinincorporated by reference in its entirety; ZSM-35 is a known zeolite andis more fully described in U.S. Pat. No. 4,016,245, herein incorporatedby reference in its entirety; and ZSM-38 is a known zeolite and is morefully described in U.S. Pat. No. 4,046,859, herein incorporated byreference in its entirety. These zeolites are known to readily adsorbbenzene and normal paraffins, such as n-hexane, and also certainmono-branched paraffins, such as isopentane, but to have difficultyadsorbing di-branched paraffins, such as 2,2-dimethylbutane, andpolyalkylaromatics, such as meta-xylene. These zeolites are also knownto have a crystal density not less than 1.6 grams per cubic centimeter,a silica-to-alumina ratio of at least 12, and a constraint index, asdefined in U.S. Pat. No. 4,229,282, incorporated by reference herein inits entirety, within the range of 1 to 12. The foregoing zeolites arealso known to have an effective pore diameter greater than 5 angstromsand to have pores defined by 10-membered rings of oxygen atoms, asexplained in U.S. Pat. No. 4,247,388, herein incorporated by referencein its entirety. Such zeolites are preferably utilized in the acid form,as by replacing at least some of the metals contained in the ionexchange sites of the zeolite with hydrogen ions. This exchange may beaccomplished directly with an acid or indirectly by ion exchange withammonium ions followed by calcination to convert the ammonium ions tohydrogen ions. In either case, it is preferred that the exchange be suchthat a substantial proportion of the ion exchange sites utilized in thecatalyst support be occupied with hydrogen ions.

The most preferred intermediate pore crystalline molecular sieve thatmay be used as part of the catalyst of the invention is a crystallinesilica molecular sieve essentially free of aluminum and other Group IIIAmetals. (By "essentially free of Group IIIA metals" it is meant that thecrystalline silica contains less than 0.75 percent by weight of suchmetals in total, as calculated as the trioxides thereof, e.g., Al₂ O₃).The preferred crystalline silica molecular sieve is a silica polymorph,such as the material described in U.S. Pat. No. 4,073,685. One highlypreferred silica polymorph is known as silicalite and may be prepared bymethods described in U.S. Pat. No. 4,061,724, the disclosure of which ishereby incorporated by reference in its entirety. Silicalite does notshare the zeolitic property of substantial ion exchange common tocrystalline aluminosilicates and therefore contains essentially nozeolitic metal cations. Unlike the "ZSM family" of zeolites, silicaliteis not an aluminosilicate and contains only trace proportions of aluminaderived from reagent impurities. Some extremely pure silicalites (andother microporous crystalline silicas) contain less than about 100 ppmwof Group IIIA metals, and yet others less than 50 ppmw, calculated asthe trioxides.

In the preferred embodiment of the invention, the crystalline molecularsieve is intimately admixed with a porous, inorganic, amorphousrefractory oxide such as alumina, to produce a high surface area supportupon which the hydrogenation metal component is subsequently deposited.The proportion of molecular sieve in the support typically varies in therange of 2 to 90 percent by weight, but preferably the support consistsessentially of a heterogeneous dispersion of the molecular sieve in amatrix of alumina or other amorphous porous refractory oxide. Such adispersion contains the molecular sieve in a minor proportion, usuallybetween about 15 and 45 percent, and more usually between 20 and 40percent, by weight, with 30 percent being most highly preferred.

The amorphous matrix portion of the support material is typicallycomprised of such amorphous inorganic refractory oxides as silica,magnesia, silica-magnesia, zirconia, silica-zirconia, titania,silica-titania, alumina, silica-alumina, etc. Mixtures of the foregoingoxides are also contemplated, especially when prepared as homogeneouslyas possible.

The most highly preferred amorphous refractory oxide for use in thecatalyst of the invention is a dispersion of silica-alumina in a matrixcontaining, but more preferably consisting essentially of, alumina. Suchdispersions are described in U.S. Pat. Nos. 4,097,365 and 4,419,271,both of which are herein incorporated by reference in their entireties.One convenient method for preparing the amorphous matrix portion of thesupport herein is to comull an alumina hydrogel with a silica-aluminacogel in hydrous or dry form. The cogel is preferably homogenous and maybe prepared in a manner such as that described in U.S. Pat. No.3,210,294. Alternatively, the alumina hydrogel may be comulled with a"graft copolymer" of silica and alumina that has been prepared, forexample, by first impregnating a silica hydrogel with an alumina saltand then precipitating alumina gel in the pores of the silica hydrogelby contact with ammonium hydroxide. In the usual case, the cogel orcopolymer (either of which usually comprises silica in a proportion bydry weight of 20 to 96 percent, preferably 50 to 90 percent) is mulledwith the alumina hydrogel such that the cogel or copolymer comprises 5to 75 weight percent, preferably 20 to 65 weight percent, of themixture. The overall silica content of the resulting dispersion on a drybasis is usually between 1 and 75 weight percent, preferably between 10and 60 weight percent.

The molecular sieve/amorphous matrix support material is usuallyprepared in the form of shaped particulates, with the preferred methodbeing to extrude a precursor of the desired support through a die havingopenings therein of desired size and shape, after which the extrudedmatter is cut into extrudates of desired length. The support particlesmay also be prepared by mulling (or pulverizing) a precalcined amorphousrefractory oxide to a particle size less than about 100 microns and thenadmixing therewith the desired molecular sieve. In the highly preferredembodiment in which the amorphous matrix portion of the support containsa dispersion of silica-alumina in a matrix containing alumina, a mulledmixture of alumina gel with either a silica-alumina cogel or a silicaand alumina "graft copolymer" may be utilized in the gel form or may bedried and/or calcined prior to combination with the molecular sieve. Inthe preferred method of preparation, the cogel or copolymer isspray-dried and then crushed to a powdered form, following which thepowder is mulled with the molecular sieve powder. The amounts of cogelor copolymer mulled with the halogenated catalytic component are suchthat the support will ultimately contain the molecular sieve anddispersion in the proportions set forth hereinbefore. If the amorphousmatrix support is not capable of sufficiently binding with the molecularsieve, a suitable binder, such as peptized Catapal^(TM) alumina, may beadmixed with the molecular sieve and refractory oxide prior toextrusion.

The extruded particles may have any cross-sectional shape, i.e.,symmetrical or asymmetrical, but most often have a symmetricalcross-sectional shape, preferably a cylindrical or polylobal shape. Thecross-sectional diameter of the particles is usually about 1/40 to about1/8 inch, preferably about 1/32 to about 1/12 inch, and most preferablyabout 1/24 to about 1/15 inch. Among the preferred catalystconfigurations are cross-sectional shapes resembling that of athree-leaf clover, as shown, for example, in FIGS. 8 and 8A of U.S. Pat.No. 4,028,227. Preferred clover-shaped particulates are such that each"leaf" of the cross-section is defined by about a 270° arc of a circlehaving a diameter between about 0.02 and 0.05 inch. Other preferredparticulates are those having quadralobal cross-sectional shapes, as inFIG. 10 of U.S. Pat. No. 4,028,227.

Typical characteristics of the molecular sieve/amorphous matrix supportsutilized herein are a total pore volume, average pore diameter andsurface area large enough to provide substantial space and area todeposit the active metal components. The total pore volume of thesupport, as measured by conventional mercury porosimeter methods, isusually about 0.2 to about 2.0 cc/gram, preferably about 0.4 to about1.5 cc/gram, and most preferably about 0.5 to about 0.9 cc/gram. Surfacearea is typically between about 250 and 600 m² /gm, preferably between350 and 480 m² /gm.

To prepare the mild hydrocracking catalyst, the support material iscompounded, as by impregnation of calcined molecular sieve/amorphousmatrix support particles, with one or more precursors of at least onecatalytically active hydrogenation metal component. The impregnation maybe accomplished by any method known in the art, as for example, by sprayimpregnation wherein a solution containing the metal precursors indissolved form is sprayed onto the support particles. Another method isthe circulation or multi-dip procedure wherein the support material isrepeatedly contacted with the impregnating solution with or withoutintermittent drying. Yet another method involves soaking the support ina large volume of the impregnation solution, and yet one more method isthe pore volume or pore saturation technique wherein support particlesare introduced into an impregnation solution of volume just sufficientto fill the pores of the support. On occasion, the pore saturationtechnique may be modified so as to utilize an impregnation solutionhaving a volume between 10 percent less and 10 percent more than thatwhich will just fill the pores.

If the active metal precursors are incorporated by impregnation, asubsequent or second calcination, as for example at temperatures between750° F. and 140° F., converts the metals to their respective oxideforms. In some cases, calcinations may follow each impregnation ofindividual active metals. Such multiple impregnation-calcinationprocedures, however, may be avoided in alternative embodiments of theinvention, as for example, by comulling all the active metals with thesupport materials rather than impregnating the metals thereon. Incomulling, precursors of the support materials, usually a mixtureincluding the molecular sieve and the amorphous matrix in a hydrated orgel form, are admixed with precursors of the active metal components,either in solid form or in solution, to produce a paste suitable forshaping by known methods, e.g., pelleting, extrusion, etc. A subsequentcalcination yields a mild hydrocracking catalyst containing the activemetals in their respective oxide forms.

When the mild hydrocracking catalyst is prepared by the foregoing orequivalent methods, at least one active metal component havinghydrogenation activity, typically one or more metal components from theGroup VIB and VIII metals of the Periodic Table of Elements, isintroduced into the catalyst. Preferably, the catalyst contains both aGroup VIB and VIII element as hydrogenation metals, with cobalt ornickel and molybdenum or tungsten being the preferred combination ofactive metals, and nickel and tungsten being most preferred. Thecatalyst contains up to about 10, usually from 1 to 8 percent, andpreferably from 2 to 6 percent by weight of the Group VIII metal,calculated as the monoxide, and up to about 30, usually from about 3 toabout 28 percent, and preferably from 8 to 26 percent by weight of theGroup VIB metal, calculated as the trioxide. A highly preferred catalystuseful herein contains about 5 to about 30 weight percent of Group VIBmetal components, calculated as the trioxide, and from about 0.5 toabout 8 weight percent of Group VIII metal components, calculated as themonoxide (Note: if molybdenum is selected as the active metal, itgenerally is solubilized with phosphoric acid during the preparation ofthe catalyst. Therefore, molybdenum-containing catalysts will usuallyfurther contain a phosphorus component on the catalyst, which phosphoruscomponent may provide acid properties to the catalyst or act as acatalytic promoter.)

Catalysts are activated in accordance with methods suited to a mildhydrocracking process. Most of the catalysts used in the mildhydrocracking process of the invention are more active, sometimes evenfar more active, in a sulfided form than in the oxide form in which theyare generally prepared. Accordingly, the catalyst used herein may besulfided prior to use (in which case the procedure is termed"presulfiding"), for example, by passing a sulfiding agent over thecatalyst prepared in the calcined form. Temperatures between 300° and700° F. and gaseous space velocities between about 140 and 500 v/v/hrare generally employed, and this treatment is usually continued for atleast about two hours. A mixture of hydrogen and one or more componentsselected from the group consisting of sulfur vapor and sulfur compounds(e.g., lower molecular weight thiols, organic sulfides, and especiallyH₂ S) is suitable for presulfiding. Generally speaking, the relativeproportion of hydrogen in the presulfiding mixture is not critical, withany proportion of hydrogen ranging between 1 and 99 percent by volumebeing adequate. Also, liquid sulfiding agents, such as dimethyldisulfide and the like, may be used for presulfiding.

If the catalyst is to be used in a sulfided form, it is preferred that apresulfiding procedure be employed. However, since mild hydrocrackingcan be employed to upgrade sulfur-containing hydrocarbons (i.e.,hydrodesulfurization), one may, as an alternative, accomplish thesulfiding in situ with sulfur-containing hydrocarbon oils, particularlythose containing about 1.0 weight percent or more of sulfur, under mildhydrocracking conditions.

The typical and preferred catalyst ultimately used for mildhydrocracking herein is essentially free of an acid halogen component,such as fluorine or chlorine. Preferably, the catalyst consistsessentially of one or more active hydrogenation metals or compoundsthereof, an intermediate pore molecular sieve, and a porous refractoryoxide. The most preferred catalyst, as disclosed in U.S. Pat. No.4,428,862, herein incorporated by reference in its entirety, consistsessentially of a sulfided catalyst containing nickel and tungsten on asupport of silicalite and a dispersion of silica-alumina in agamma-alumina matrix, with a binder material being present if desired.

The mild hydrocracking catalyst may be employed as either a fixed,slurried or fluidized bed (but most usually a fixed bed) of particulatesin a suitable reactor vessel wherein the hydrocarbon oil to be treatedis introduced and subjected to mild hydrocracking conditions includingan elevated total pressure, temperature, and hydrogen partial pressure.Under such conditions, the hydrocarbon oil and catalyst are subjected toa hydrogen partial pressure usually less than 1,500 p.s.i.g. (frequentlyless than about 1,200 p.s.i.g. for vacuum gas oil mild hydrocracking) ata space velocity usually less than 3.0 LHSV so as to effect the desireddegree of hydrocracking, desulfurization, and denitrogenation. As usedherein, "mild hydrocracking" requires the conversion of about 10 toabout 50 volume percent of the feedstock hydrocarbons boiling aboveabout 700° F. to products boiling at or below 700° F. from a single passof the feedstock. Preferably, mild hydrocracking conditions are suchthat at least a 15 volume percent conversion is obtained, and usually nomore than a 35 volume percent conversion is obtained.

Contemplated for treatment by the process of the invention arerelatively high boiling hydrocarbon-containing oils including crudepetroleum oils and synthetic crudes. Among the typical oils contemplatedare top crudes, vacuum and atmospheric residual fractions, light andheavy atmospheric and vacuum distillate oils, shale oils, and oils frombituminous sands, coal compositions and the like. For use herein,typical hydrocarbon oils, or mixtures thereof, contain at least about 50volume percent of components normally boiling above about 700° F.

Generally, a substantial proportion (i.e., at least about 90 volumepercent) of hydrocarbon feeds such as gas oils and the like boil at atemperature less than about 1100° F., preferably less than about 1050°F., and usually boil entirely within the range of about 100° F. to about1100° F., and most frequently in the range from about 500° F. to about1100° F.

Although virtually any high boiling hydrocarbon feedstock may be treatedby mild hydrocracking, the process is particularly suited to treating(1) gas oils, preferably light and heavy vacuum gas oils and waxy shaleoils, and (2) heavy residual fractions, especially the treatedatmospheric and vacuum residuum oils containing less than about 25 ppmwof contaminant metals (vanadium, nickel, and the like). Sulfur isusually present in such oils in a proportion exceeding 0.1 weightpercent and often exceeding 1.0 weight percent. Frequently, thefeedstock contains undesirable proportions of nitrogen, usually in aconcentration greater than about 0.01 weight percent and often betweenabout 0.01 and 1.0 weight percent. The feedstock may contain waxycomponents, e.g., n-paraffins and isoparaffins, and thus have a highpour point, e.g., at least about 30° F.

A hydroprocessing reactor useful in the mild hydrocracking process ofthe invention is ordinarily an existing reactor that is part of anexisting hydroprocessing unit, or units, in a refinery. A preferredreactor is one formerly used for vacuum gas oil desulfurization. In themild hydrocracking of such a gas oil, the catalyst is usually maintainedas a fixed bed with the feedstock passing downwardly once therethrough,and the reactor is generally operated under conditions within the limitsof the existing reactor design. In some instances, mild hydrocrackingreactors may be added to the existing equipment, either in series orparallel. If the feedstock is unusually high in organonitrogen andorganosulfur compounds, it may be pretreated, integrally or separately,using a hydrotreating catalyst.

Typical mild hydrocracking conditions that yield more than about 10volume percent conversion of the oil fraction boiling above 700° F. toliquid products boiling at or below 700° F. are shown in the followingTable I:

                  TABLE I                                                         ______________________________________                                                                      Preferred                                       Operating Conditions                                                                            Suitable Range                                                                            Range                                           ______________________________________                                        Temperature, °F.                                                                         500-900     600-850                                         Hydrogen Pressure, p.s.i.g.                                                                       200-1,500   500-1,300                                     Space Velocity, LHSV                                                                            0.05-3.0    0.1-1.5                                         Hydrogen Recycle Rate, scf/bbl                                                                    500-15,000                                                                                1000-10,000                                   ______________________________________                                    

Generally, the hydrogen partial pressure maintained during hydrocrackingis more than 50 percent of the total pressure. Usually, for once-throughoperation, the hydrogen partial pressure is between about 85 and 95percent of the total pressure while, for recycle operation, the hydrogenpartial pressure is somewhat lower, i.e., between 80 and 85 percent ofthe total pressure.

Another preferred reactor utilized in the process of the invention is ahydrodesulfurization reactor formerly used for processing a hydrocarbonresiduum feedstock. Ordinarily, this reactor is in the latter stage, orstages, of a multi-stage unit for hydrodesulfurization and/ordemetallization of a residuum-containing feedstock. In the case of mildhydrocracking a residuum feedstock, the hydrogen partial pressure isusually higher than that during mild hydrocracking a gas oil. Incomparison to conventional hydrodesulfurization conditions that yield,from a single pass, less than about 10 volume percent of liquidhydrocarbon products boiling at or below 700° F., the operatingconditions of the process of the invention for mild hydrocracking aresiduum hydrocarbon typically include an increased temperature and/ordecreased space velocity, correlated to effect a conversion greater than10 percent.

The results obtained in any particular mild hydrocracking process willdepend upon the nature of the catalyst, the nature of the feedstock, andthe severity of the operating conditions. Also, it is highly preferredthat about 15 to about 35 volume percent of the oil is converted, in asingle pass, to liquid products boiling at or below 700° F., and that atleast about 85 volume percent of the 700° F. minus fraction containliquid hydrocarbon products boiling in the midbarrel range from about300° F. to about 700° F.

The invention is further illustrated by the following examples which areillustrative of specific modes of practicing the invention and are notintended as limiting the scope of the invention defined by the appendedclaims.

EXAMPLE I

Two catalysts were prepared in accordance with the invention. The firstcatalyst, Catalyst A, was prepared by extruding a mixture of 30 weightpercent silicalite, 50 weight percent gamma alumina, and 20 weightpercent Catapal™ alumina binder through a die with 1/16-inch diameteropenings. The extruded matter, having a cylindrical shape, was brokeninto particulates, dried at 930° F., and then impregnated with nickelnitrate (Ni(NO₃)₂.6H₂ O) and ammonium metatungstate so as to incorporateinto the catalyst, after drying and a calcination at 900° F., about 4weight percent nickel components, calculated as NiO, and about 22 weightpercent tungsten components, calculated as WO₃.

The second catalyst, Catalyst B, was prepared in the same manner asCatalyst A except that, instead of gamma alumina, a dispersion ofsilica-alumina in alumina was utilized. The dispersion was itselfprepared by mixing about 60 parts by dry weight of a 75/25silica-alumina graft copolymer with about 40 parts by weight of hydrousalumina gel. Overall, the dispersion consisted essentially of 48 percentby weight silica and 52 percent by weight of alumina.

Both catalysts were tested for their activity for mild hydrocracking thehydrocarbon feedstock identified in the following Table II.

                  TABLE II                                                        ______________________________________                                        Feedstock Properties                                                          ______________________________________                                        Feed Description Light Arabian Vacuum Gas Oil                                 Gravity, °API                                                                           22.3                                                         Sulfur, wt. %    2.54                                                         Nitrogen, wt. %  0.09                                                         Carbon Residue, D-189, wt. %                                                                   0.42                                                         Pour Point, °F.                                                                         +95                                                          ASTM D-1160, Vol. %                                                                            Distillation, °F.                                     IBP/5            623/700                                                      10/20            737/776                                                      30/40            810/837                                                      50/60            860/898                                                      70/80            928/968                                                      90/95            1019/1056                                                    EP               1103                                                         ______________________________________                                    

The test was conducted by contacting the catalysts in separate runs withthe feedstock identified in Table II under mild hydrocrackingconditions. However, at the outset of each run, the respective catalystswere presulfided by contact for about 16 to 20 hours with a gasconsisting of 90 volume percent H₂ and 10 volume percent H₂ S flowing at4.4 SCFM (one atmosphere pressure). The temperature during thepresulfiding is initially at room temperature, is increased graduallyuntil 700° F. is reached, and then lowered to 550° F., at which time thecatalyst is contacted with the feedstock.

A portion of the feedstock is passed downwardly through a reactor vesseland contacted with the described catalysts in a single-stage,single-pass system with once-through hydrogen. The operating conditionsduring each run are summarized as follows: 1,000 p.s.i.g. totalpressure, 1.0 LHSV, a hydrogen rate of 3,000 SCF/bbl, and temperatureadjusted to determine the conversions obtainable at 710°, 735°, and 755°F. The conversions obtained for each catalyst are set forth in thefollowing Table III, with it being noted that conversion was calculatedas the volume percentage of material boiling above 700° F. converted tomaterial boiling at or below 700° F.

                  TABLE III                                                       ______________________________________                                                Volume Percent Conv.                                                          of 700° F.+ to                                                         Lower Boiling Products                                                Catalyst  710° F.                                                                             735° F.                                                                        755° F.                                 ______________________________________                                        A         17.5         20.6    25.1                                           B         17.5         22.5    29.9                                           ______________________________________                                    

The data in Table III clearly indicate that both catalysts are usefulfor mild hydrocracking a typical gas oil feedstock. In addition, thedata obtained at 735° F. and 755° F. evince the superiority of CatalystB containing the dispersion of silica-alumina in alumina over theotherwise identical Catalyst A containing alumina.

EXAMPLE II

A hydrocracking catalyst of the invention was prepared in the samemanner as Catalyst B of Example I except that SAPO-11 was employed asthe intermediate pore molecular sieve. This catalyst, designatedCatalyst C, was tested under the mild hydrocracking conditions and withthe feed described in Example I and the data obtained for activity,sulfur conversion, and nitrogen conversion against a commercial mildhydrocracking catalyst run under the same conditions and the same feedare set forth in the following Table IV:

                  TABLE IV                                                        ______________________________________                                        Conversion to  Wt. % Sulfur Wt. % Nitrogen                                    700° F.- at                                                                           at           at                                                Temp. °F.                                                                             Temp. °F.                                                                           Temp. °F.                                  710      735    755    710  735  755  710  735  755                           ______________________________________                                        Com-  18.0   22.6   29.6 --   0.23 0.113                                                                              0.040                                                                              0.024                                                                              0.015                       mercial                                                                       Cata-                                                                         lyst                                                                          Cata- 19.1   25.0   33.3 0.48 0.20 0.12 0.042                                                                              0.024                                                                              0.016                       lyst C                                                                        ______________________________________                                    

Based on the data in Table IV, the catalyst of the invention is markedlysuperior to the commercial catalyst for converting the feed to 700° F.-products and at least comparable in its activity for desulfurization anddenitrogenation.

Although the invention has been described in conjunction with itspreferred embodiment and examples, many variations, modifications, andalternatives will be apparent to those skilled in the art. For example,although the foregoing catalysts were described in relation to theirparticular usefulness for mild hydrocracking, it is clear from thediscoveries in the present invention that such catalysts may also beused for hydrocracking, either alone or in conjunction with conventionalwide pore hydrocracking catalysts. Also, although numerous intermediatepore molecular sieves have been disclosed for use in the invention,still others are contemplated, as, for example, organosilicate molecularsieves as disclosed in U.S. Pat. No. 4,104,294, herein incorporated byreference in its entirety, and the metallo-organosilicate molecularsieves disclosed in U.S. Pat. No. Re. 29,948, provided, of course, thatthe sieve chosen for use has a pore size between 5 and 7 angstroms.Accordingly, it is intended to embrace within the invention all suchvariations, modifications, and alternatives as fall within the spiritand scope of the appended claims.

I claim:
 1. A process for mild hydrocracking a hydrocarbon feedstockcomprising contacting said feedstock containing feed components boilingabove 700° F. under conditions of elevated temperature and pressure lessthan about 1,500 p.s.i.g. with a particulate catalyst comprising atleast one active hydrogenation metal component selected from the groupconsisting of Group VIB and Group VIII metals in combination with (1) adispersion of silica-alumina in a matrix consisting essentially ofalumina and (2) a crystalline intermediate pore molecular sievecomprising a silicoaluminophosphate having a pore size between about 5and 7 angstroms, said conditions yielding about a 10 to about a 50volume percent conversion of said feed components boiling above 700° F.to product components boiling at or below 700° F.
 2. The process definedin claim 1 wherein said conditions include a hydrogen partial pressureless than about 1,200 p.s.i.g.
 3. A process as defined in claim 1wherein the hydrogen partial pressure is less than about 1475 p.s.i.g.and the conversion is between 15 and 30 volume percent.
 4. A process asdefined in claim 3 wherein the hydrogen partial pressure is less thanabout 1,450 p.s.i.g.
 5. The process defined in claim 1 wherein saidintermediate pore molecular sieve comprises SAO-11.
 6. The processdefined in claim 1 wherein the hydrogen partial pressure is less thanabout 1,000 p.s.i.g.
 7. The process defined in claim 1 wherein saidconversion is between about 15 and about 35 volume percent.
 8. Theprocess defined in claim 6 wherein said conversion is between about 15and about 35 volume percent.
 9. The process defined in claim 5 whereinsaid conversion is between about 15 and about 35 volume percent.
 10. Theprocess defined in claim 1 wherein said conversion is between about 15and about 30 volume percent.
 11. The process defined in claim 10 whereinsaid hydrogenation component comprises a combination of a Group VIB andGroup VIII metals.
 12. The process defined in claim 5 wherein saidhydrogenation metal component comprises at least one metal selected fromthe group consisting of nickel and cobalt and at least one metalselected from the group consisting of molybdenum and tungsten.
 13. Theprocess defined in claim 6 wherein said hydrogenation metal componentcomprises at least one metal selected from the group consisting ofnickel and cobalt and at least one metal selected from the groupconsisting of molybdenum and tungsten.
 14. The process defined in claim9 wherein said hydrogenation metal component comprises at least onemetal selected from the group consisting of nickel and cobalt and atleast one metal selected from the group consisting of molybdenum andtungsten.
 15. A process for mild hydrocracking a hydrocarbon feedstockcomprising feed components boiling above 700° F. comprising contactingsaid feedstock under conditions of elevated temperature and a hydrogenpartial pressure less than about 1,500 p.s.i.g. with a particulatecatalyst comprising at least one Group VIII active metal hydrogenationcomponent and at least one Group VIB active metal hydrogenationcomponent on a support comprising (1) a dispersion of silica-alumina ina matrix consisting essentially of gamma alumina and (2) a crystallineintermediate pore silicoaluminophosphate molecular sieve of about 5 toabout 7 angstroms pore size, said conditions yielding between about a 10and 50 volume percent conversion of the feed components boiling above700° F. to product components boiling at or below 700° F.
 16. Theprocess defined in claim 15 wherein said hydrogen partial pressure isless than 1,200 p.s.i.g.
 17. The process defined in claim 15 whereinsaid intermediate pore molecular sieve comprises SAPO-11.
 18. Theprocess defined in claim 17 wherein the hydrogen partial pressure isless than about 1,000 p.s.i.g.
 19. The process defined in claim 18wherein said conversion is between about 15 and about 35 volume percent.20. The process defined in claim 18 wherein said conversion is betweenabout 15 and about 30 volume percent.
 21. A process for mildhydrocracking a hydrocarbon feedstock selected from the group consistingof a gas oil and residuum containing a substantial proportion of feedcomponents boiling below about 1100° F. with a least some of said feedcomponents boiling above 700° F., under conditions of elevatedtemperature and a hydrogen partial pressure between about 500 p.s.i.g.and about 1,500 p.s.i.g. with a catalyst comprising at least one GroupVIII active metal hydrogenation component and at least one Group VIBactive metal hydrogenation component on a support comprising incombination (1) a dispersion of silica-alumina in a matrix consistingessentially of gamma alumina and (2) a crystalline intermediate poresilicoaluminophosphate molecular sieve of about 5 to 7 angstroms poresize, said conditions being such that between about 10 and 50 percent byvolume of said feed components boiling above 700° F. are converted toproduct components boiling at or less than 700° F.
 22. A process asdefined in claim 21 wherein between about 15 and 35 percent by volume ofsaid feed components boiling above 700° F. are converted to productcomponents boiling at or below 700° F.
 23. A process as defined in claim22 wherein said hydrogen partial pressure is less than about 1,200p.s.i.g.
 24. A process as defined in claim 21 wherein said intermediatepore molecular sieve has a pore size between about 5 and 6 angstroms.25. A process for mild hydrocracking a hydrocarbon feedstock comprisingsaid feedstock containing feed components boiling above 700° F. underconditions of elevated temperature and pressure less than about 1,500p.s.i.g. with a particulate catalyst comprising at least one activehydrogenation metal component selected from the Group consisting ofGroup VIB and Group VIII metals in combination with (1) a dispersion ofsilica-alumina in a matrix consisting essentially of alumina and (2) anintermediate pore molecular sieve comprising a crystalline silica havinga pore size between about 5 and 7 angstroms, said conditions yieldingabout a 10 to a 50 volume percent conversion of said feed componentsboiling above 700° F. to product components boiling at or below 700° F.26. A process as defined in claim 25 wherein said catalyst comprisesboth Group VIII and Group VIB active hydrogenation components.
 27. Aprocess as defined in claim 26 wherein said pressure is above 500p.s.i.g.
 28. A process as defined in claim 27 wherein said catalystcomprises both nickel and tungsten hydrogenation components.
 29. Aprocess as defined in claim 28 wherein said intermediate pore molecularsieve is silicalite.
 30. A process as defined in claim 29 wherein saidconversion is between 15 and 35 volume percent.
 31. A process as definedin claim 30 wherein the hydrogen partial pressure is less than about1,000 p.s.i.g.
 32. A process as defined in claim 29 wherein the hydrogenpartial pressure is between 500 and 1,200 p.s.i.g.